This appears to be two different parametrizations of the same surface. When
you Show them together Mathematica has difficulty in rendering them because
it has to keep determining which surface is 'in front'.
I don't understand what you are trying to illustrate in your plot.
David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/
From: Narasimham [mailto:mathma18 at hotmail.com]
To: mathgroup at smc.vnet.net
a) How to make ParametricPlot3D to plot in the required PlotRange for
top half surface only?
b) How to omit/hide circumferential circles or parameter lines of al
in Show[pos,neg] ? TIA
<<RealTime3D`
pos=ParametricPlot3D[ {Cosh[th] Cos[th+al], th, Cosh[th]Sin[th+al]},
{th,-1.2, 1.2 }, {al,0, 2 Pi} ,PlotRange-> { { -2,2},{2,0},{0,2} } ];
neg=ParametricPlot3D[ {Cosh[th] Cos[th+al], th, -Cosh[th]Sin[th+al]},
{th,-1.2, 1.2 }, {al,0, 2 Pi} ,PlotRange-> { { -2,2},{2,0},{0,2} } ];
Show[pos,neg] ;
<<Default3D`